A Hybrid Na//K + -Containing Electrolyte//O 2 Battery with High Rechargeability and Cycle Stability.

Na-O-2 and K-O-2 batteries have attracted extensive attention in recent years. However, the parasitic reactions involving the discharge product of NaO2 or K anode with electrolytes and the severe Na or K dendrites plague their rechargeability and cycle stability. Herein, we report a hybrid Na//K+-containing electrolyte//O-2 battery consisting of a Na anode, 1.0 M of potassium triflate in diglyme, and a porous carbon cathode. Upon discharging, KO2 is preferentially produced via oxygen reduction in the cathode with Na+ stripped from the Na anode, and reversely, the KO2 is electrochemically decomposed with Na+ plated back onto the anode. The new reaction pathway can circumvent the parasitic reactions involving instable NaO2 and active K anode, and alternatively, the good stability and conductivity of KO2 and stable Na stripping/plating in the presence of K+ enable the hybrid battery to exhibit an average discharge/charge voltage gap of 0.15 V, high Coulombic efficiency of >96%, and superior cycling stability of 120 cycles. This will pave a new pathway to promote metal-air batteries.